This program hopes to delineate some of the molecular determinants of transepithelial Na ion and K ion transport, as well as the metabolic pacemaker activity of cation transport. The primary hormonal regulator of Na ion, K ion, and H ion excretion in the urine is aldosterone. Previous studies indicate that aldosterone induces the synthesis of mitochrondrial enzymes and in particular citrate synthase. We now propose to study the possibility that aldostrone also regulates Na ion conductance of the apical surface plasma membrane by inducing changes in protein or lipid composition. Techniques have been devised for covalent labeling (125I) and substantial purification of the apical plasma membrane of toad bladder epithelium. Double isotope incorporation studies into amiloride-labeled and structural apical proteins and into membrane phospholipids and lipids will be attempted. The effects of aldosterone, and of glucocorticoids on the kidney are initiated by binding to specific cytoplasmic receptors. To analyze the mechanism of receptor mediated induction of RNA synthesis, new steroid analogs will be used for site specific labeling and purification of the labeled receptors. The intent is to use the purified receptors in identification of the primary induction events leading to the action on conservation of salt. A second phase of the research involves the role of thyroidal induction of the Na ion pump in the heart, kidney and liver as a mediator of the thermogenic response. The planned studies include the mechanisms of augmented synthesis of the small and large subunits of the Na ion pump and the role of induction of mRNA versus post-translational processing in this response. These studies may provide new insights into hormonal mechanisms operating in patients with hypertension, and congestive heart failure or other edematous states.